There was a few times in his first run when he injured himself or other people, He dropped A-Train on his head and broke Bob Holly's neck not sure if that was all his fault though depends who's story you believe, As far as him being unsafe I don't think he's as unsafe as anyone else on the roster the only difference is Brock could kill anyone on the roster so if he botches a move or hits a bit to stiff your going to know about it.

The only guy i wouldn't put him in the ring with is Undertaker and thats only because with the shape Undertaker is in Brock might really hurt him if he goes out there and has the same type of match he had with Cena and HHH